Contact adhesives differ from other adhesives, such as pressure sensitive adhesives, in that the adhesives are applied to both substrates to be joined and then dried. These adhesives are characterized by a bonding range or "open time", i.e. the period after the adhesive is dried during which adhesive coated substrates can be successfully joined and bonded. Contact adhesives are used to manufacture decorative laminates.
Environmental regulations require a reduction in solvent emissions in the decorative laminate industry. Solvent based neoprene contact adhesives, the industry standard, are a primary source of these emissions. Attempts have been made to reduce solvent volatiles through the use of aqueous contact adhesives or high solids solvent-based adhesives. However, in both cases some solvent is necessary in the adhesive to achieve the requisite performance, particularly tack. Those completely solvent free adhesives which have been offered are of inferior performance.
JP 62-50595 discloses an adhesive composition for interior decoration materials used in vehicles comprising 3 to 100 wt parts of hollow glass particles with a particle density of 0.05 to 0.5 g/cm.sup.3 and a mean particle size of 10 to 100 microns, 100 wt parts of a macromolecular latex (solid matter), and no more than 300 wt parts of a thermoplastic resin powder.
U.S. Pat. No. 4,748,061 discloses pressure sensitive adhesive tape in which the adhesive layer can either be filled with microbubbles or have a cellular core. Example 6 shows the use of polymeric microbubbles made from a copolymer of vinylidene chloride and acrylonitrile in a syrup of coatable viscosity prepared by partially photopolymerizing a mixture of isooctyl acrylate and acrylic acid to which hexanediol diacrylate, polymeric microbubbles and carbon black are added. Example 1 uses glass microbubbles in the same syrup. EP 0 349 216 A discloses an acrylate pressure sensitive adhesive tape, several examples of which contain Expancel 551 DEK polymeric microspheres. The phase-separated, ultra violet-radiation polymerized, pressure sensitive adhesives comprise
a) about 70 to 98 parts of an acrylic copolymer, and PA1 b) 30 to about 2 parts of a hydrocarbon elastomer or blend of hydrocarbon elastomers containing at least one segment having a lower Tg than the acrylic copolymer, wherein the adhesive has at least a first phase and a second phase, the first phase consisting primarily of the elastomer, and preferably being a continuous phase. PA1 a) an aqueous emulsion of an adhesive polymer, PA1 b) 0-50 wt % plasticizer, based on adhesive polymer, PA1 c) 0.5-10 wt % thermoplastic hollow microspheres, based on adhesive polymer, and PA1 d) 0-4.5 wt % polyethylenimine, based on adhesive polymer,
U.S. Pat. No. 3,316,187 discloses aqueous binder compositions for bonding, sealing and caulking of masonry units (tile, cement block, cinder block, red brick, etc.). The composition comprises an ambient temperature curable liquid synthetic resin and an ambient temperature curing agent therefor; an elastomeric agent for the composition, and a cellular organic filler material known as phenolic microballoons.